Why simulate GNSS signals?

During the development and testing of electronic systems incorporating global navigation satellite systems such as GPS, Galileo, BeiDou or GLONASS, it is very useful to have position, velocity and time data being fed into the system under test, to evaluate how well the system operates.

Static GPS Testing

If you are interested only in static tests, then you can use a live antenna to provide the feed to the GPS engine. The disadvantage of this method is that the signal changes all the time, so you can't reproduce the same conditions twice.

By using GPS simulation you get the same signal strengths, satellite numbers, atmospheric effects and UTC time whenever the test is run, making benchmarking and testing much more consistent.

Dynamic GPS Testing

If your application involves moving the system under test, to assess it in a dynamic environment, then normally you would need to fit your electronics to the target vehicle or aircraft, and test in the field. This is expensive and time consuming, and conditions change each time the procedure is run.

By using a GPS simulator with a dynamic scenario, you can replay the moving data directly into the GPS engine under test as many times as you like.

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How to make GNSS testing realistic yet repeatable

If you have a very specific dynamic test, you have several options:

Record from a live antenna, using a GPS RF Recorder

Create the scenario artificially using a user defined trajectory and then replay through a GPS RF Replay unit

Use a dedicated full constellation simulator

With these methods, the GPS data is identical every time the test is run - including all of the signal strengths, the number of satellites in view, the time of the test, and the exact path taken by the vehicle.

You save a lot of time, expense, and inaccuracies by testing on the bench rather than taking the system out in the field each time!

What GPS simulators are available?

There are three types of simulator:

GPS engine simulators

RF signal record/replay simulators

Full constellation simulators

GPS Engine Simulators

GPS engine simulators are the most basic option, and generate the same output as a GPS / GLONASS engine, normally in the form of a serial NMEA type message. To use this kind of simulator, the GNSS engine is removed completely from the target system and the signals are injected into the rest of the circuit. These are used mainly by system integrators who are not interested in the performance of the GNSS engine itself. These simulators are generally software, and output data on a serial port.

GPS RF Record / Replay systems

RF record/replay systems, such as RACELOGIC’s LabSat, sample the RF signal from a live GPS/GLONASS/Galileo/BeiDou/QZSS antenna(s) at a very high rate and store this to a hard drive digitally. This data can then be replayed directly into the RF front end of a GPS/GLONASS/Galileo/BeiDou/QZSS engine, faithfully reproducing the original signal.

Full Constellation Simulators

Full constellation simulators, such as RACELOGIC’s SatGen software, generate all satellite signals from scratch. This is combined with a user defined trajectory file to create an artificial GPS signal. This can be done in real time using dedicated (but expensive) hardware, or processed offline on a normal PC which then creates a data file which can be replayed using a more simple record/replay system.

How to record, replay, and simulate GNSS Signals

LabSat is an RF Record/Replay system, which will capture real world, realistic data, and play it back as many times as required for testing. RACELOGIC also produce the SatGen simulation software, which has the ability to create a full constellation scenario, and then replay it using LabSat.

Who can benefit from a GNSS recorder, replayer, and simulator?

LabSat is designed for GPS chipset test and development, GNSS system integrators across industries as diverse as automotive, defence, marine, and government. Manufacturers of GNSS devices even use LabSat at events to demonstrate their products to end users, and in the testing of faulty units.

The ability for LabSat to integrate with RACELOGIC’s Video VBOX offers video synchronisation alongside the GNSS data, while the use of external modules allows external data to be recorded from a variety of sources, offering many testing possibilities.

LabSat is now used by leading OEM and mobile device companies such as Bosch, Garmin, Nokia, RIM, and Thales to test their devices in real world yet repeatable conditions. Have a look at some of LabSat’s users (Customer Profiles tab).